rpm-autosign.exp:  New utility to help sign rpms.

The rpm commend insists on prompting for a passphrase when signing rpms even
for passphraselees keys.  This behaviour causes problems for automated build
scripts.  The rpm-autosign.exp scripts is a small expect wrapper for rpm that
that sends empty passphrase in reposne to the prompt.

Signed-off-by: Gary Lowell  <gary.lowell@inktank.com>